Christoph Hauert

Department of Zoology, UBC

Cooperation in social dilemmas: Volunteering in public goods games

Cooperative behavior among unrelated individuals is one of
the fundamental problems in biology and social sciences.
Reciprocal altruism fails to provide a solution if interactions
are not repeated often enough or groups are too large. Punishment
and reward can be very effective but require that defectors can
be traced and identified. Here we present a simple but effective
mechanism operating under full anonymity. Voluntary participation
in public goods games can foil exploiters and overcome the social
dilemma. This natural extension leads to rock-scissors-paper type
cyclic dominance of the three strategies cooperate, defect and
loner i.e. those unwilling to participate in the public enterprise.
In voluntary public goods interactions the three strategies can
co-exist under very diverse assumptions on population structure
and adaptation mechanisms. In particular, spatially structured
populations, where players interact only with their nearest
neighbors, lead to interesting dynamical properties and
intriguing spatio-temporal patterns. Variations of the value
of the public good result in transitions between one-, two-
and three-strategy states which are in the class of directed
percolation. Although volunteering is incapable of stabilizing
cooperation, it efficiently prevents successful spreading of
selfish behavior and enables cooperators to persist at
substantial levels.

Refreshments will be served at 2:45 p.m. in the Faculty Lounge,
Math Annex (Room 1115).